JP2004320912A - Switching power supply - Google Patents

Abstract

An active filter and a DC / DC converter can be sequentially activated by a single activation circuit, and a hunting operation when an input voltage gradually decreases is reliably prevented.
A diode (D2) connected to a power supply line (20) of an AF control circuit (7) and a converter control circuit (14) for interrupting power supply from the AF control circuit connection point to the converter control circuit connection point; A start-up circuit 8 that supplies a start-up voltage to the start-up choke coil 6 after the start-up of the active filter 3; A rectifier circuit 9 supplies the rectified circuit 9 to the AF control circuit 7 for continuous operation and a power obtained by rectifying the output of the auxiliary winding L5 of the insulating transformer 11 after the DC / DC converter 4 is started. A rectifier circuit 16 for continuous operation, and activates the active filter 3 and the DC / DC converter 4 sequentially when the power is turned on. That. The switch 18 is turned off after the start, and prohibits the restart after the DC / DC converter 4 stops.
[Selection diagram] Fig. 1

Description

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply in which a DC / DC converter is arranged after an active filter for improving a power factor.
[Prior art]
2. Description of the Related Art Conventionally, as this type of switching power supply, for example, there is one shown in FIG.
In FIG. 2, the switching power supply receives a commercial AC voltage of 100 V from input terminals 1a and 1b, performs full-wave rectification by a diode bridge 2, and then inputs the active filter 3 to an active filter 3 for improving a power factor. Is input to the DC / DC converter 4, and the voltage supplied from the output terminals 13a and 13b to the load is stabilized.
The active filter 3 includes an inverter element 5, a boost choke coil 6 having a main winding L1 and an auxiliary winding L2, an AF control circuit 7, a rectifying circuit having a diode D1 and a capacitor C1, a starting circuit 8, and a control power supply. A rectifier circuit 9 is provided. That is, the active filter 3 controls the average current of the current waveform connecting the peaks of the switching current due to the switching of the inverter element 5 to be in phase with the full-wave rectified AC voltage waveform. The noise level is reduced by suppressing the emission of noise to the outside.
The DC / DC converter 4 includes an inverter element 10, a primary winding L3, a secondary winding L4, an insulating transformer 11 having an auxiliary winding L5, a rectifying circuit 12 for output, a converter control circuit 14, a start-up circuit 15, A rectifier circuit 16 for a control power supply is provided. Converter control circuit 14 controls switching of inverter element 10 such that output voltage Vo from rectifier circuit 12 becomes a predetermined voltage.
In the conventional circuit shown in FIG. 2, when the power to which the AC input is applied is turned on, the active filter 3 and the DC / DC converter 4 are sequentially activated in the following manner.
When the AC input voltage is applied, the active filter 3 is activated by the activation voltage supplied from the activation circuit 8 to the AF control circuit 7, and is activated via the diode D <b> 1 by the boost operation of the boost choke coil 6 by the switching control of the inverter element 5. As a result, the voltage obtained between both ends of the capacitor C1 increases.
The voltage of the capacitor C1 is supplied as a start-up voltage from the start-up circuit 15 to the converter control circuit 14, and the converter control circuit 14 starts up, controls the switching of the inverter element 10 to control the propagation of the power energy of the insulating transformer 11, and 12 stabilizes the output voltage Vo supplied to the load.
[Patent Document 1]
Japanese Patent Application Laid-Open No. H10-337023 [Problems to be Solved by the Invention]
However, in such a conventional circuit, when the input voltage to the active filter 3 gradually decreases, the input current increases because the output power is constant, and as a result, the overcurrent protection operation of the active filter 3 finally results. Since the inverter element 5 is turned off, the boosted output voltage obtained across the capacitor C1 decreases, and the DC / DC converter 4 also stops.
When the DC / DC converter 4 stops, the overcurrent protection operation of the active filter 3 is released, the inverter element 5 of the active filter 3 is switched again to restart the inverter operation, and the boosted output voltage to the DC / DC converter 4 increases. Then, the operation of restarting the DC / DC converter 4 is repeated. This appears as a hunting operation in which the output voltage is turned on and off at a constant cycle, and the user load may malfunction.
In order to prevent the hunting operation in which the output voltage is repeatedly turned on and off at a constant cycle, as shown in FIG. 2, a low-input stop circuit that accurately detects a drop in the input voltage and stops the active filter 3. 17 must be provided, but such a circuit requires a precise setting of the hysteresis between the start voltage and the stop voltage, and therefore requires a high-precision circuit and has a problem that the circuit configuration becomes complicated.
In addition, two systems of starting circuits for connecting the starting circuits 8 and 15 to the high-voltage sections on the input sides of the active filter 3 and the DC / DC converter 4 are required. 15 requires a predetermined creepage distance, which increases the installation space and hinders miniaturization. In addition, since the two startup circuits are always operating, there is a problem that the loss is also large.
On the other hand, in order to prevent a hunting operation in which the output voltage is repeatedly turned on and off at a constant cycle due to a decrease in the input voltage, there is a circuit in which the active filter and the DC / DC converter have a single startup circuit and the startup and the stop are synchronized. (See Patent Document 1).
In this conventional circuit, a boosted output voltage obtained at both ends of a capacitor provided at the output of an active filter is supplied to both an AF control circuit and a converter control circuit to start up, and after startup, the active filter and the inverter of the DC / DC inverter are started. The operation of each control circuit is continued by the rectified output of each auxiliary winding by the operation.
When the AC input is temporarily cut off and the boosted output voltage stops, both control circuits are operated with the charge voltage of the capacitor, and when the capacitor charge voltage drops to a predetermined value and the active filter stops, , The DC / DC converter is also forcibly stopped.
However, in such a conventional circuit in which starting and stopping are synchronized, the starting circuit can be simplified as a single circuit to reduce the size of the circuit, but when the input voltage gradually decreases, the DC / DC converter If the power supply stops first, the load on the active filter is reduced, the boosted output voltage is restored, and the DC / DC converter is restarted repeatedly, and the output voltage is turned on and off, thus completely eliminating the problem. It has not been.
In addition, since the active filter and the DC / DC inverter are started in synchronization with each other, the inrush current at the time of starting is large, and it is necessary to increase the current capacity of the active filter that is generating the starting power. There is also a problem to do.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply that enables sequential activation of an active filter and a DC / DC converter with a single activation circuit and reliably prevents hunting operation when the input voltage gradually decreases. I do.
[Means for Solving the Problems]
To achieve this object, the present invention is configured as follows. The present invention provides an active filter for improving a power factor including a boost choke coil, an inverter element, and an active filter control circuit (AF control circuit), and an insulating transformer, an inverter element, and a converter control circuit connected to the active filter. A switching power supply device provided with a DC / DC converter provided.
The present invention for such a switching power supply device is connected to a power supply line for supplying operating power to the active filter control circuit and the converter control circuit, and supplies power from the active filter control circuit connection point to the converter control circuit connection point. A diode to cut off, a start-up circuit that supplies a start-up voltage to the active filter control circuit when the power is turned on, and a start-up circuit. And a first rectifier circuit for supplying power to the active filter control circuit via a diode to continue the operation, and supplying power obtained by rectifying the output of the auxiliary winding of the isolation transformer to the converter control circuit after the DC / DC converter is started. And a second rectifier circuit for continuously operating the It characterized by being configured to sequentially start the active filter and the DC / DC converter when.
Therefore, regardless of the combination of the activation voltage of the active filter control circuit and the activation voltage of the converter control circuit, the DC / DC converter can always be activated after the activation of the active filter. This increases the degree of freedom in circuit arrangement. In addition, by sequentially activating the active filter and the DC / DC converter, an inrush current at the time of activation can be reduced.
In the switching power supply of the present invention, the switch inserted and connected to the power supply line from the first rectifier circuit to the converter control circuit and the switch that is turned on before the start of the converter control circuit are turned off after the start. A switch control circuit that cuts off power supply from the first rectifier circuit, detects a stop of input voltage to the active filter and turns on the switch, and prohibits restart when the DC / DC converter stops. It is characterized by having done.
Therefore, when the input voltage to the active filter gradually decreases and the DC / DC converter stops, the restart of the DC / DC converter is prohibited regardless of the operation of the active filter, and the output voltage is turned on and off at a constant cycle. Prevents repeated hunting operation.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a circuit diagram showing an embodiment of the switching power supply device according to the present invention.
In FIG. 1, the switching power supply receives a commercial AC voltage of 100 V from input terminals 1a and 1b, performs full-wave rectification by a diode bridge 2, and then inputs the active filter to an active filter 3 for improving a power factor. Is input to the DC / DC converter 4, and the voltage supplied from the output terminals 13a and 13b to the load is stabilized.
The active filter 3 includes an inverter element 5, a boost choke coil 6 having a main winding L1 and an auxiliary winding L2, an AF control circuit 7, a rectifying circuit having a diode D1 and a capacitor C1, a starting circuit 8, and a control power supply. A rectifier circuit 9 is provided.
That is, the active filter 3 drives the main winding L1 of the boost choke coil 6 to drive the main winding L1 to turn on the inverter element 5 to supply a switching current to maintain energy, and to turn off the inverter element 5 to turn on the main winding L1 of the boost choke coil 6. To output a boosted voltage to the capacitor C1 via the diode D1, and this is repeated.
Therefore, control is performed so that the average current of the current waveform connecting the peaks of the switching current flowing when the inverter element 5 is turned on and off is in the same phase as the full-wave rectified AC voltage waveform. To reduce the noise level by suppressing radiation to the outside.
The DC / DC converter 4 includes an inverter element 10, a primary winding L3, a secondary winding L4, an insulating transformer 11 having an auxiliary winding L5, a rectifying circuit 12 for output, a converter control circuit 14, and a control power supply. A rectifier circuit 16 is provided.
The DC / DC converter 4 is not provided with a dedicated activation circuit, and supplies a voltage obtained by the inverter operation after the activation of the active filter 3 to the converter control circuit 14 by supplying the activation voltage to the converter control circuit 14.
For this purpose, a power supply line 20 for supplying a start-up voltage to the AF control circuit 7 and the converter control circuit 14 to start the operation, and for supplying operation maintaining power after the start-up is provided. Are connected at point P, the rectifier circuit 9 is connected at point Q, the converter control circuit 14 is connected at point R, and the rectifier circuit 15 is further connected.
The diode D2 is connected between the connection points P and Q of the power supply line 20, and cuts off the supply of the starting voltage from the starting circuit 8 to the converter control circuit 14. Therefore, the starting voltage of the starting circuit 8 is supplied only to the AF control circuit 7.
On the other hand, the rectifier circuit 9 that performs rectification output based on the output of the auxiliary winding L2 by the inverter operation after the activation of the active filter 3 supplies power to both the AF control circuit 7 and the converter control circuit 14, and When viewed from above, it functions as a starting circuit.
A switch 18 that can be turned on and off by an external signal is connected between a point Q and a point R of the power supply line 20. A switch element such as a transistor or a MOS-FET is used as the switch 18.
The switch 18 is controlled by the switch control circuit 22 and is turned on before the DC / DC converter 4 starts, and turned on when the converter control circuit 14 starts. The switch 18 that has been turned off by the activation is reset by a detection signal when it is detected from the input voltage stop detection circuit 21 provided at the input of the active filter 3 that the divided voltages of the resistors R1 and R2 become substantially 0V. It is turned on.
The converter control circuit 14 receives the rectified power from the rectifier circuit 9 when the active filter 3 is started, and starts. Therefore, the DC / DC converter 4 is activated only after the active filter 3 is activated, and the sequential activation of the active filter 3 and the DC / DC converter 4 is ensured.
The converter control circuit 14 started by the rectification output from the rectification circuit 9 controls the switching of the inverter element 10 so that the output voltage Vo from the rectification circuit 12 becomes a predetermined voltage.
Next, the operation of the embodiment of FIG. 1 will be described. When an AC input is applied to the input terminals 1a and 1b by turning on the power, the output voltage of the starting circuit 8 increases due to the full-wave rectified output of the diode bridge 2 and when the predetermined starting voltage is reached, the AF control circuit 7 starts, and the inverter operation by the switching of the inverter element 5 is started.
When the inverter operation of the active filter 3 is started, the rectifier circuit 9 generates a rectified output by the output of the auxiliary winding L2 of the boost choke coil 6, and is activated by the converter control circuit 14 via the switch 18 which is turned on at this time. When power is supplied and the supply voltage reaches a start-up voltage, the converter control circuit 14 starts and stabilizes the output voltage Vo by switching of the inverter element 10.
When the converter control circuit 14 is started, it outputs a start signal to the switch control circuit 22. Therefore, the switch control circuit 22 turns off the switch 18 and cuts off the power supply from the active filter 3 side.
If the input voltage to the active filter 3 gradually decreases in this state, the input current increases because the output power is constant, and as a result, the inverter element 5 is turned off by the overcurrent protection operation of the active filter 3. In this state, the boosted output voltage obtained at both ends of the capacitor C1 decreases, and the DC / DC converter 4 also stops.
When the DC / DC converter 4 stops in this way, the overcurrent protection operation of the active filter 3 is released, and the inverter element 5 of the active filter 3 is switched again to restart the inverter operation, and the boosted output to the DC / DC converter 4 is increased. The voltage rises, and a rectified output from the rectifier circuit 9 is also obtained.
However, since the switch 18 is off, the rectified output of the rectifier circuit 16 is not supplied to the converter control circuit 14, the restart of the DC / DC converter 4 is prohibited, and the output voltage is turned on and off at regular intervals. Prevent repeated hunting operations.
The reset of the restart inhibition of the DC / DC converter 4 can be performed by temporarily cutting off the AC input. When the AC input is temporarily cut off, the input voltage of the active filter 3 also temporarily becomes substantially 0 V. This is detected by the input voltage stop detection circuit 21 and a detection signal is output to the switch control circuit 22 to output the detection signal to the switch 18. Is reset from off to on.
Therefore, the rectified output of the rectifier circuit 9 by the activation of the active filter 3 is supplied to the converter control circuit 14 via the switch 18, and the DC / DC converter is activated.
Note that the present invention includes appropriate modifications that do not impair the objects and advantages thereof.
【The invention's effect】
As described above, according to the present invention, the DC / DC converter can always be activated after the activation of the active filter, regardless of the combination of the activation voltage of the active filter control circuit and the activation voltage of the converter control circuit. A single starting circuit connected to the high voltage section increases the degree of freedom in circuit arrangement. In addition, by sequentially activating the active filter and the DC / DC converter, an inrush current at the time of activation can be reduced.
In addition, only one activation circuit is required for the active filter and the DC / DC converter, and since two activation circuits are connected to the high voltage section, the problem of ensuring a creepage distance is solved, and miniaturization of the circuit and reduction of loss are reduced. Can be planned.
Further, when the input voltage to the active filter gradually decreases and the DC / DC converter stops, the restart of the DC / DC converter is prohibited, and a hunting operation in which the output voltage is repeatedly turned on and off at regular intervals can be prevented.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a circuit diagram showing a conventional circuit.
1a, 1b: input terminal 2: diode bridge 3: active filter (AF)
4: DC / DC converters 5, 10: Inverter element 6: Boost choke coil 7: AF control circuit 8: Starting circuits 9, 12, 16: Rectifying circuit 11: Insulating transformers 13a, 13b: Output terminal 14: Converter control circuit 18 : Switch 20: power supply line 21: input voltage stop detection circuit 22: switch control circuit L1: main winding L2, L5: auxiliary winding L3: primary winding L4: secondary winding D1, D2: diode C1: Capacitors R1, R2: resistance

Claims (2)

An active filter for power factor improvement comprising a boost choke coil, an inverter element and an active filter control circuit;
A DC / DC converter connected to the active filter and provided with an isolation transformer, an inverter element, and a converter control circuit;
In a switching power supply device having
A diode that is connected to a power supply line that supplies operating power to the active filter control circuit and the converter control circuit, and that shuts off power supply to the converter control circuit connection point from the active filter control circuit connection point side;
A start-up circuit that supplies a start-up voltage to the active filter control circuit at power-on to start the active filter control circuit,
After the activation of the active filter, the power obtained by rectifying the output of the auxiliary winding of the boost choke coil is supplied to the converter control circuit to be activated and supplied to the active filter control circuit via the diode to continue the operation. One rectifier circuit,
A second rectifier circuit that supplies the power obtained by rectifying the output of the auxiliary winding of the insulating transformer after the start of the DC / DC converter to the converter control circuit to continue the operation;
Wherein the active filter and the DC / DC converter are sequentially activated when the power is turned on. The switching power supply according to claim 1, further comprising:
A switch inserted and connected to the power supply line from the first rectifier circuit to the converter control circuit;
A switch that turns off the switch that is on before starting the converter control circuit, turns off the switch after the start, cuts off power supply from the first rectifier circuit, detects the stop of input voltage to the active filter, and turns on the switch. A control circuit;
Wherein the switching power supply device is configured to prohibit restart when the DC / DC converter is stopped.

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